1. Field of the Invention
This invention relates to methods of making heat-resistant equipment and systems and more specifically to methods of making a new non-segregating solid-reinforced composite for use in heat-resistant electronic equipment or systems.
2. Description of Related Art
Different industries urgently demand equipment and systems which operate efficiently at high temperatures. Thermal stress often limits component, system, and equipment performance or life. Such industries include: automotive, electronics, aerospace, health, education, communication, defense, and entertainment. In this invention, the electronics industry will be primarily used as an example.
Today's $1 trillion electronics market is the world's largest and most strategically important industry. The industry provides various electronic components for fast computers, satellite communication systems, deep-well drilling equipment, jet engines, gas turbines, and other systems or equipment. The industry also provides critical components for appliances such as cellular phones, computers, instruments, entertainment devices, educational systems, transportation vehicles, and other articles of mass manufacture.
Electronic components or systems are often mechanically attached together or to the systems frame by screwing, bolting, or clamping. Alternately, the components are chemically or metallurgically bonded together by gluing, soldering, brazing, or welding, depending on the operating temperature of the system and equipment. Often the operating temperature is close to the melting or softening point of the component materials or bonding medium (glue, solder, braze, or weldment). Such a high temperature causes rapid thermal and electrical degradation of the bonded region due to creep, fatigue, and other failure modes.
Semiconductor wafers, chips and circuit boards have many metallic layers or lead wires and lines to conduct electricity. The lead wires or lines must be as few in number and as short as possible to reduce electrical resistances. Electrical resistances slow down the speed of electronic systems. These metallic components must also be rigid, strong, fatigue-resistant, creep-resistant, and thermally conductive to help dissipate heat. Excessive heat generation from, for example, electrical resistances, increases the system temperature, reduces the life of transistors, lowers the mechanical strength and creep resistance of metallic components, and degrades chip and system performance.
Various materials of the mechanically or chemically connected components on the electronic system or equipment are always mismatched in coefficients of thermal expansion (CTE). Metals often have CTE's that are over two to over ten times greater than ceramics such as SiC, Al.sub.2 O.sub.3, SiB.sub.6, or even semiconductor silicon; but smaller than those of plastics such as encapsulating epoxy or circuit board substrate. Hence, significant thermal mismatch stresses always arise between the various components materials when the system is thermally cycled over a temperature range, e.g., over 200-250.degree. C., due to in-circuit power on/off switching.
Heat decreases material strength and increases thermal or electrical resistivities of materials. High thermal resistances decrease heat dissipation, increase the operating temperature, and degrade the semiconductor properties. High electrical resistances adversely affect localized heat generation and life, performance and the clock rate of computers. A 10.degree. C. increase in temperature exponentially decreases semiconductor component life and doubles the chemical reaction rate of, e.g., the formation of high-resistance, crack-initiating intermetallic compounds (IMC) in the chemically bonded regions. These inherent material, thermal, electrical, and chemical factors synergistically intensify one another's effect causing run-away failures of the electronic materials, components, systems, and equipment.
In an electrical circuit board or system, one therefore always has to consider the ever-present thermal mismatch stresses due to mismatched CTE's of components materials. When any electronic equipment and system changes in temperature, thermal mismatch stresses are generated between:
1) the semiconductor wafer or chip and the mounting head on which this wafer or chip is mounted; PA1 2) the metallic layers and lead wires and their encapsulating plastic; PA1 3) the metallic layers and lead wires and the bonded metal layers on the through holes of the circuit board substrate; and PA1 4) the circuit board substrate and the mounting frame of the electronic equipment and system.
Thermal design often is the limiting factor for many electronic systems. For example, the heat generated in a 233-MHz Pentium chip presents a formidable problem. This problem must be solved without discarding the existing mother-circuit-board architecture. Yet, Pentium chips with even higher speeds are already in use.
Fundamental physical, chemical, thermal, electrical, and other limitations of current on-chip interconnecting materials are driving the electronics industry to alternative technologies for "wiring" tomorrow's semiconductor wafers and devices. Heat production, high operating temperature, and thermal stress due to materials mismatch in CTE are unavoidable problems. Thermal stress even limits device miniaturization and chip clock rate, as shown below.
In particular, thermal fatigue and reduced performance is a very common failure mode of the tin-lead solder joint in bonded electronic components. The reliability of electronic packaging and on-chip or off-chip requires reducing creep and fatigue failures from temperature fluctuations and in-circuit power on/off switching.
Many factors must be considered in electronic packaging: signal integrity, CTE and thermal mismatch stress, solder particle segregation due to size or composition, solder paste screening, solder reflow and uniformly fine width, solder ball failures, chip packing density, yield, cost, package warpage, electrical and thermal performance, cleaning, rework operation, moisture resistance, assembly processes, flatness, coplanarity, board level reliability, soaring input/output counts, and extremely miniaturized device with multiple metal layers.
Also troublesome are the following soldering defects: voiding, bridging (or short), solder balling and spreading, insufficient solder, misregistration, opens from poor solder wetting or due to warpage from thermal or mechanical stressing.
Accordingly, an object of the present invention is to provide a novel bonding composite to bond together the various electronic components;
A second object of the invention is to provide a novel composite that has substantially non-segregating solid reinforcing elements;
Another object of the invention is to provide improved reinforcing elements which reinforce the composite matrix mechanically, thermally, electrically;
A further object of the invention is to provide improved reinforcing elements which have controlled anisotropic mechanical, thermal, and electrical properties;
Another object of the invention is to provide easily wetted solid reinforcing elements for improved composite performance;
A still another object of the invention is to provide reinforcing elements in tin-lead composites which can withstand many temperatures cycles between -50 to 200.degree. C.;
Yet another object of the invention is to provide advanced processes and composite materials for semiconductor manufacturing;
A further object of the invention is to provide semiconductor processing methods and materials to achieve improved device miniaturization and reliability, conductive line width and height, chip planarity and coplanarity, wafer warpage, mounting, and very high density on-chip and off-chip interconnect including semiconductor packaging and chip to board integration;
A still further object of the invention is to provide improved semiconductor wafer chips, devices, circuit boards, and systems which are smaller, thinner, lighter, faster, more cost-effective, and more reliable than existing ones;
Another object of the invention is to provide new methods and materials to overcome various chemical, mechanical, thermal, electrical, and other problems related to the electronics manufacture;
Yet another object of the invention is to provide 100% dense, voidfree (under 1000.times. magnification) graded metal-ceramic bonds to withstand temperatures close to the melting of the bonding medium.